william wrote:rockdoctor said what I feel.
I bought my first road bike only 2 years ago and on the first downhill ride the bike felt like I had a rapidly deflating tyre at 50 kph. The bike was all over the road scaring the poo out of me. A sudden stop to fix the flat and found nothing wrong.
Long story short, ugly wheels branded "Mavic Aksium Race" wheels.
I got some lovely hand built wheels and no problems since.
Bikes, if designed properly, should not have any induced wobble of any sort. If it does, get it fixed or get a properly designed bike with better wheels.
If it was simply a design issue it would have been solved long ago and no bikes would ever shimmy. If it was well understood and easily solved, the lawsuits for negligence would have made sure of that. The fact of the matter is that the rider is a large component in the system. A bike that shimmys under one rider will be rock solid under another, even if their proportions are identical.
I believe that every bike/rider combination will experience shimmy at some speed. For most riders/bikes the critical speed appears to be unattainable because they have not experienced it. The problem can't be 'solved' you just change the critical speed to something that you can't get to.
To change the critical speed requires even the smallest change. In your case it was wheels, for others the change can be made by, different tyres/tubes, different stems (presumably changing the weight distribution), sometimes even a different mental attitude. A friend of mine experienced shimmy briefly during a race, she had got away from me going uphill and was descending down the other side. She did not experience shimmy until I came past with a closing speed of 15km/h or more. What caused it? Was it my disturbing the air? My theory is that the surprise caused her to tense up a bit, changing the 'spring constant' of her arms. She went down the same hill again later in the race (at probably a similar speed) without experiencing shimmy.
Whatever solution works is a good one.